I've has my XSi for about a month now and have read WAY too many posts regarding lens options! So here I am inches away from taking the plunge for a 70-200mm F4L IS.

I just have a feeling that due to my issues with image sharpness, the 70-300mm F4-5.6 would not be able to satisfy me. My only problem may be an occasional desire for longer zoom, but I figure if I needed to, I could get the 1.4 Extender.

yes 70-200mm f/4 IS sharpness across focal length and aperture is legendary.
the size and weight is also very good for walk around. AF speed is very fast. IS make some noise when activated, but you can always turn it off when you don't need it.

One of the best lens Canon produces, it is almost perfect!

The only imperfection i find is it is not ideal shooting moving objects in low light condition. Second, the bokeh is not as easy to achieve/better comparing to f/2.8 version.

But the f/2.8 IS version is $600 different and bigger in size/weight

The other consideration is f/2.8, without IS actually i have lil bit regret not buying this lens instead of f4 IS in the first place (because kind of photography i'm involved with is more of action and portrait).

While, the f4 IS is more about general purposes. It can do many things
and deliver excellent result, but not as best as f/2.8 version in certain
condition such as sports and portraiture.

But as your first L lens you will have (like me at that time) you'll be very satisfied.

Hi everyone.
I'm new to this forum. Today I just sent out my order for the non-IS version of this lens. Cost was one of my issues. I would've loved to get the IS lens. But I will get the non-IS instead. I truly just love the Canon Cameras. This will be my very first L lens. Talk to you all later.

Hey, BNSFrailfan... I take it from your forum name that you are a rail fan esp. BNSF railways, and if you are would love to see some of the trains you have captured. As most people know on here I am a big rail fan here in the UK and use my 70-200 L IS USM a lot for railway photography at which it is absolutley brilliant, to see what I do click on my fotopic site in my siggie.